ACMA BPL emission testing at Mt Beauty, Victoria, Australia. |
Pole-mounted BPL equipment in Australia: Capacitive coupling from a medium-voltage line to a BPL repeater. The insulators contain the coupling device which takes the BPL signal off the MV line and feeds it to the repeater. |
An FSM jump kit. [WIA Photos] |
NEWINGTON, CT, Mar 7, 2007 -- It was a scenario unlikely to be played out anytime soon in the US: The Australian Communications and Media Authority (ACMA), radio amateurs and a broadband over power line (BPL) provider worked hand-in-hand to measure background noise and emissions at a BPL trial site. ACMA's late February visit was in response to a BPL interference complaint from Ian Paul, VK3LJJ. Wireless Institute of Australia (WIA) Director Phil Wait, VK2DKN, was on hand for the field tests at the Mt Beauty BPL pilot in Victoria. He said BPL service provider SP-Ausnet first deactivated the system, and ACMA performed background noise measurements at various locations around the township. Agency representatives then measured BPL emissions and the effectiveness of Amateur Radio-band notching of the BPL signal after system reactivation.
"As expected high-level BPL emission was measured in the trial area," Wait reported. "The maximum notch depth measured within amateur bands was about 35 dB. Background noise was higher than expected, highlighting the need for a series of noise measurements over many days to accurately determine typical background noise levels at any location."
Software Enables Improved Notching
During the testing, Wait says, SP-Ausnet demonstrated new network control software that allows remote notching in any part of the BPL pilot system. Observations confirmed that in the vicinity of Paul's location, SP-Ausnet has notched all affected HF amateur bands except for 10 meters, he noted. Higher-than-expected background noise on the amateur bands at the time hampered the ability to adequately determine notch depth, however.
The WIA believes that adequate notching will require both software and hardware notching to protect Amateur Radio operation from substantial BPL interference, and that should be the focus of further development by BPL equipment manufacturers.
"It is apparent that all stakeholders involved in BPL trials in Australia are now taking interference complaints from radio amateurs very seriously and are making changes to their BPL technology and systems to improve the outcome for radio amateurs," Wait said.
Tests Confirm Validity of Measurement Technique
Wait said the Mt Beauty testing provided an ideal opportunity to compare real-world data from ACMA's measuring equipment and the field strength measurement technique based on a hardware design by ARRL Lab Manager Ed Hare, W1RFI, and a companion software application FSM.exe -- Field Strength Measurement -- developed by Owen Duffy, VK1OD.
"We were able to demonstrate close agreement between the two measurement systems, thus confirming our confidence in the FSM measuring technique and our own FSM measurement jump-kit," Wait said.
The FSM technique uses a conventional SSB receiver to allow measurement and field strength calculation of radio signals or interference. The technique depends on the fact that the receiver's audio output power is linearly related to RF input -- including equivalent internal noise -- up to the onset of AGC action, typically a little more than 20 dB above the equivalent receiver input noise.
By using a known external attenuator to keep measured signals within this linear range, it's possible to make relative measurements of the receiver audio output power and calculate absolute results by factoring in the attenuator, receiver equivalent internal noise and other variables.
WIA's November 2006 Mt Beauty Tests
Last November, the WIA conducted tests of its own at the Mt Beauty BPL trial, taking measurements outside Paul's home as well as at other locations in the BPL trial area. "This report documents very high levels of interference over the 40, 30, 20 and 15-meter amateur bands," Wait said. "The interference was measured at such a level that would effectively prevent HF radio communications within the trial area on the frequencies affected."
ACMA Measures BPL Emissions at VK7HCK.
In January, ACMA performed a series BPL emission measurements and on-air observations at the home of Conrad Kley, VK7HCK, to confirm the resolution of interference complaints he'd lodged in November 2005 and September 2006. ACMA invited the WIA to observe the measurement activity.
Service provider Aurora Energy changed the BPL network characteristics in the area around Kley's residence following his initial interference complaint. Wireless backhaul is now used between BPL system repeaters, and most HF amateur bands are notched only by about 25 dB.
Among other things, ACMA took BPL emission measurements using an active loop antenna placed near electrical power service entrance and measured BPL signal voltage on the station's antenna feed line, observing the effect of the BPL emissions on Kley's HF transceiver. The ACMA measurements appeared to indicate a reduction in BPL emissions compared with previous measurements and observations.
WIA Develops BPL Interference Reporting Form
The WIA has developed a new downloadable form for Australian radio amateurs to use when lodging formal BPL interference complaints to ACMA. For use in conjunction with the WIA's BPL Interference Advisory Service, the form takes into account that Amateur Radio terminology often differs from that used professionally, eg ACMA logs received signal strength readings in dBuV (decibels above or below one microvolt), rather than S units.
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